This disclosure relates to adjusting noise reduction in headsets or headphones.
Active noise reduction (ANR) headphones, such as those described in U.S. Pat. No. 7,412,070, use electronics to create anti-noise signals that cancel the ambient noise as it reaches the wearer's ear. Headphones that contact the head around the ear are referred to as circum-aural, while those that rest directly on the external ear, also known as the pinna of the ear, are referred to as supra-aural. ANR headphones may be circum-aural, supra-aural, or in-the-ear, and typically employ some passive noise reduction measures to provide noise reduction beyond the bandwidth and energy level provided by the active electronics. A set of circum-aural headphones 10 is shown in FIG. 1A for reference. Such headphones have two earcups 12 and 14, each with a cushion 16, 18 that contacts the wearer's head. In supra-aural headphones, the cushions would contact the wearer's external ear. The earcups 12 and 14 are connected to each other by a headband 20 via yokes 22 and 24. Other configurations are also used, such as a direct connection between the end of the headband and the earcups, without a yoke, or a band referred to as a “nape band” that goes behind the wearer's neck rather than over the head.
ANR headphones may use feedback, feedforward, or some combination of the two to generate the anti-noise signals, as shown, for example, in FIG. 1B. In the example of FIG. 1B, an ANR circuit 100 receives input from a feed-forward microphone 102, a feedback microphone 104, and an audio input 106. Implementations may include any or all of these or additional inputs. The signals from the feedforward and feedback microphones are passed through filters 108 and 110 which produce anti-noise signals. The anti-noise signals are combined with any audio input signals, as indicated by summing node 112, amplified by an amplifier 114, and provided as output signals 116 to an electroacoustical transducer 118, also known as a driver or speaker. In some examples, more than one output transducer is used. ANR headphones may also provide audio for entertainment and communication, and may use the same or additional speakers as are used for generating the anti-noise signal to do so. ANR headphones may also reproduce sounds detected by microphones on the exterior of the earcup to allow the user to hear sounds in the environment when desired. This feature is sometimes called talk-through. Feedforward ANR headphones that provide talk-through features may use the same microphones for both feedforward noise cancellation and talk-through, or may have separate microphones for each feature. The signal paths and relative locations and numbers of components in FIG. 1B are merely one example. The various signal paths, such as feedforward and feedback, may each have dedicated amplifier stages applying different gains. ANR circuit 100 may be implemented in analog or digital electronics, or some combination of both.
Passive noise reduction headsets use mechanical measures to reduce the amount of ambient noise reaching the ear of the wearer. These mechanical measures generally consist of acoustic insulation that is placed in the earcups or that is placed in the ear to block the ear canal. For supra-aural and circum-aural headsets, a major factor affecting the amount of noise reduction, beyond the properties of the insulating material itself, are how well the earcups seal to the ears or head of the wearer. The force applied to press the earcups against the wearer's head, referred to as clamping force, is one of several factors that affects the quality of the seal. Other factors are the compliance of the cushion between the earcup and the ear or head, and whether any leaks exist, either between the cushion and the wearer or through parts of the earcup. In some examples, leaks are intentionally provided in order to control the acoustic properties of the headset. Passive noise reduction headsets may include electronic components for reproducing audio, for any or all of entertainment audio, electronic communications, or to provide talk-through using external microphones.